Dennis caught the eye of many after he scored twice against Real Madrid at the Santiago Bernabeu in a Champions League encounter in 2019.
However, he had a disappointing campaign last season. The 23-year-old played nine times for Club Brugge last in the first half of the campaign and got into trouble on a few occasions.
He was sent out on loan to Cologne in January with the hope he could rediscover the form that saw him score against Madrid and Manchester United in the 2019/2020 season.
But the move did not turn out well for the Nigerian international, playing just nine times in the Bundesliga.
Cologne’s former sporting director even admitted they made a mistake in signing the Super Eagles star.
Nonetheless, a move to Watford offers him another fresh start and Premier League opportunity. The Hornets are back in the English top-flight after suffering relegation in the 2019/2020 campaign.
Dennis latest move means Watford now have four Nigerians in their team. William Troost-Ekong, Tome Dele Bashiru and Isaac Success are the other three Nigerian players already playing for the club.